Lifestyles have become increasingly reliant on mobile communications. Wireless communication devices, such as cellular phones, laptop computers, pagers, personal communication systems (PCS), personal digital assistants (PDA), and the like, provide advantages of ubiquitous communication without geographic or time constraints, as well as the added security of being able to contact help in the event of an emergency. Mobile terminals have been equipped with versatile location-awareness technologies, such as global position system (GPS) tracking features. Such features enable a consumer to monitor the position of the terminal as well as transmit its location to emergency response personnel during emergency situations.
The position of a device is monitored through GPS technologies that utilize a system of orbital satellites to determine positioning information. The constellation of satellites will transmit very low power interference and jamming resistant signals to a wireless device GPS receiver, which may receive signals from multiple satellites at once. The GPS receiver may determine three-dimensional spatial positioning information from GPS signals obtained from at least four satellites. These GPS signals are transmitted over two spread spectrum microwave carrier signals that are shared by the GPS satellites. Measurements from satellite tracking and monitoring stations located around the world are incorporated into orbital models for each satellite to compute precise orbital or clock data. Thus, a wireless device employing a GPS receiver identifies GPS signals from at least four satellites, decodes the ephemeris and clock data, determines a pseudo range for each satellite, and then computes the position of the receiving antenna of the GPS receiver. Accordingly, the spatial position of the receiving antenna can be determined with great accuracy and convenience.
Unfortunately, since GPS signals are transmitted over two low power spread spectrum microwave carrier signals, the GPS receiver must have an unobstructed “view” of the GPS satellites. Indoor environments, e.g., buildings, cellars, edifices, garages, pavilions, or other urban settings, obstruct the “field of view” of the GPS receiver, and GPS tracking becomes unreliable. Tracking is unavailable when the GPS signals are too weak or cannot reach the GPS receiver.
Conventional location-awareness technologies are further limited by an inability to identify the vertical location of a device in a multistory building. While planar positioning may be obtainable, there is no provision for defining accurate three dimensional spatial coordinate positions. Emergency response personnel can arrive at an appropriate address in response to an emergency call, but lose valuable time to precisely locate where in the building help is required.
Accordingly, a need exists for positioning tools and methodology that enable users in obstructed areas to determine more accurately and/or report their positions. The particular need to derive absolute three-dimensional position can be of critical importance.